Engines operating with a variable number of active or deactivated cylinders may be used to increase fuel economy, while optionally maintaining the overall exhaust mixture air-fuel ratio about stoichiometry. In some examples, half of an engine's cylinders may be disabled during selected conditions, where the selected conditions can be defined by parameters such as a speed/load window, as well as various other operating conditions including vehicle speed. A VDE control system may disable selected cylinders through the control of a plurality of cylinder valve deactivators that affect the operation of the cylinder's intake and exhaust valves.
Various approaches have been identified for diagnosing degradation in VDE operation, such as based on crankshaft vibrations related to engine firing order, firing frequency, etc. However, the inventors herein have recognized several disadvantages with such approaches. As an example, such approaches may be unable to identify particular situations, such as when one cylinder valve of a cylinder is properly deactivated, but another valve in the same cylinder continues to operate even when it is commanded to be deactivated. As another example, such approaches may be unable to identify situations where one cylinder valve of a cylinder is properly activated, but another valve in the same cylinder fails to operate even when it is commanded to be activated. As yet another example, such approaches may be unable to identify situations where both valves in a single cylinder continue to operate even when they are commanded to be deactivated.
Thus, in one example, the above issues may be at least partially addressed by a method of monitoring cylinder valve deactivation in an engine operating with a plurality of cylinder valves, the method comprising, indicating valve degradation based on an indication of manifold pressure over a plurality of immediately successive induction events of the engine, said indication responsive to increases and decreases in the indication of manifold pressure correlated to the induction events of engine cylinders, and further correlated to whether cylinders are commanded to be activated or deactivated.
In one example situation, a cylinder is commanded to be activated, and while an exhaust valve of the cylinder is properly activated, an intake valve does not lift during the intake stroke. Herein, no induction event occurs even though an induction event was expected for the cylinder's intake stroke. As such, the non-operation of the intake valve will cause substantially no intake air to be drawn into the cylinder and compressed. As a result, the change in manifold pressure associated with that intake stroke of that cylinder may be significantly different (for example, significantly higher) from the expected change in manifold pressure. The expected change in manifold pressure for a given cylinder's intake stroke may be determined statistically based on corresponding changes in manifold pressure (during corresponding intake strokes) for cylinders that fire before and/or after the monitored cylinder, in the engine cycle.
In another example situation, a cylinder is commanded to be deactivated, and both an exhaust valve and an intake valve continue to lift during the intake stroke. Herein, an induction event occurs even though no induction event was expected for the cylinder's intake stroke. As such, the operation of the intake and exhaust valves will cause a substantial amount of intake air to be drawn into the cylinder and compressed. As a result, the change in manifold pressure associated with that intake stroke of that cylinder may be significantly different (for example, significantly lower) from the expected change in manifold pressure.
By monitoring the manifold pressure response during the intake stroke of each cylinder, and by comparing an average change in manifold pressure during a first sampling window (for example, the first 90 crank degrees) and a second sampling window (for example, the last 90 crank degrees) of an intake stroke, valve activation/deactivation degradation may be identified. Specifically, if the change in manifold pressure for the monitored cylinder is significantly different from a statistically determined change in manifold pressure during an intake stroke for all the other cylinders, the nature of valve degradation may be further identified. In this way, by comparing a change in manifold pressure associated with each intake stroke of a cylinder with a statistically determined expected pressure change based on the response of other cylinders, and further based on the expected presence or absence of an induction event, valve degradation associated with VDE operations can be identified and distinguished.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.